It is known that a seat belt apparatus installed in a vehicle such as an automobile restrains an occupant by a seat belt in case of such an emergency as described above to prevent the occupant from jumping out of a seat.
Such a seat belt apparatus is provided with a seat belt retractor that winds a seat belt. In the seat belt retractor, the seat belt is wound around a spool when not worn. When the seat belt is to be worn, the seat belt is withdrawn and is fastened around an occupant. In case of the emergency mentioned above, a locking mechanism included in the seat belt retractor is actuated to lock the rotation of the spool in a seat belt withdrawal direction, whereby the withdrawal of the seat belt is prevented. Thus, the occupant is restrained by the seat belt in case of an emergency.
In the above known seat belt retractor of the seat belt apparatus, when the seat belt restrains the occupant in case of emergency, such as a vehicle collision, a rapid vehicle deceleration occurs to cause the occupant to move forward due to a large inertia.
Accordingly, a large load is applied to the seat belt and a large energy is applied to the occupant from the seat belt. The energy is not particularly a problem to the occupant but, if possible, it is desirable that the energy is restricted.
Accordingly, conventionally, a seat belt retractor has been developed that is provided with a torsion bar so that, in a state where the seat belt is worn in an emergency situation, energy is absorbed and alleviated with the load acting on the seat belt restricted.
However, in conventional seat belt retractors, only a single limit load is set for the limit load after the collision. In actuality, the energy applied to the occupant differs in various manners depending on the weight and the like of the occupant. Rather than responding to such different kinds of large energies with a single limit load, by setting limit loads according to the circumstances of the vehicle in an emergency, the occupant can be restrained in a more effective and adequate manner.
To meet the above requirement, there is proposed a seat belt retractor provided with first and second energy absorbing mechanisms so as to be able to change the limit load applied to the seat belt by setting one or two limit loads according to the circumstances of an emergency (see, for example, Patent Document 1).